The present invention addresses three problems: (1) the lack of stability of geosynthetic clay liners on slopes or embankments; (2) the problems associated with the use of adhesives or glue in the manufacture of geosynthetic clay liners; and (3) the requirement imposed by needlepunching process that at least one nonwoven fabric be employed in the construction of the geosynthetic clay liner.
The concept of using bentonite to create a low permeability layer for use in landfills and man-made bodies of water is well known. Bentonite is a naturally occurring clay material which expands upon being exposed to water. When dry bentonite is wetted and thereafter expands, the bentonite is capable of substantially precluding the migration of liquids through it if properly contained.
It is also well known to provide bentonite in sheet or roll form by gluing or adhering bentonite to a sheet of textile material, hereinafter known as the primary carrier sheet. Another term used interchangeably with primary carrier sheet is primary textile. An upper layer of textile material may be provided thereby disposing the bentonite between two layers of textile material. The upper layer is hereinafter referred to as the cover sheet. Other terms used interchangeably with cover sheet include secondary textile, secondary carrier sheet and scrim. The bentonite in roll-form is often referred to as a geosynthetic clay liner by those skilled in the art.
Geosynthetic clay liners (GCLs) provided in rolls are easily applied to large surface areas, such as a landfill or a man-made pond or lake, by simply unrolling the liners in a manner similar to the laying of carpet. When the bentonite is exposed to water it expands between the two textile sheets and forms a barrier with a very low permeability.
At least three problems are associated with the above technique for providing a barrier with a geosynthetic clay liner made from bentonite disposed between two textile sheets. The first problem relates to slope stability. The primary carrier sheet and the cover sheet may be made from woven fabrics that are relatively smooth. The bentonite itself becomes very slippery when it is hydrated. Without interconnection between the textile fabric layers, the geosynthetic clay liners may lack slope stability.
A second problem relates to the cost of using glue or adhesive as a means for attaching the various components of a geosynthetic clay liner together. This method of attachment is expensive because of time and energy requirements. First, the glue must be applied to the primary carrier. Then the bentonite is placed on the prepared carrier. Once the bentonite is applied to the wet glue, the glue must dry, a procedure which requires expensive equipment and which has significant energy expenses. While the use of glue has the benefit of holding the bentonite granules in place, use of glue as the sole means for holding the liner together requires repeated applications of glue and entails substantial energy in the drying process.
The prior art also teaches needlepunching and quilting as the means of initially attaching the bentonite to the primary carrier sheet. A needlepunching process requires the use of at least one nonwoven fabric for the cover sheet or the primary carrier sheet. The nonwoven fibers are pulled by the needles to interlock with the adjacent fabric sheet. Nonwoven fabrics have lower tensile strengths than woven fabrics and have higher lateral transmissivity than woven fabrics and therefore it is not as preferable to use nonwoven fabrics as woven fabrics in geosynthetic clay liners.
Thus, there is a need for an improved geosynthetic clay liner that includes bentonite disposed between a primary carrier sheet and a cover sheet which may be applied to, and retain its position, on a steep bank or slope of the landfill site or pond. There is also a need for an improved geosynthetic clay liner that can be manufactured either without the need for gluing or a reduced dependency on gluing the bentonite to the primary carrier sheet and further without using nonwoven materials.